Background: To clarify the landscape of molecular diagnoses (MDs) in early-onset epilepsy individuals, we determined the prevalent MDs stratified by age at seizure onset (SO) and the time to MD in children with SO <36 months of life. Methods: A panel of up to 302 genes associated with epilepsy was utilized and ordering physicians provided the age of SO. Diagnostic yield analyses were performed for SO ages including <1 mo, 1-2 mo, 3-5 mo, 6-11 mo, 12-23 mo, and 24-35 mo. The time to MD (MD age - SO age) was determined for the top 10 genes in each SO category. Results: 15,074 individuals with SO <36 months of life were tested. Predominant MD findings are as follows: KCNQ2 in neonates with SO at <1mo, KCNQ2 and CDKL5 for SO between 1-2 mo, PRRT2 and SCN1A for SO between 3-11 mo, and SCN1A for SO between 12-36 months. The median time to MD varied by gene. For example, there was no delay in the median time to MD for the GLDC, KCNQ2, and SCN2A genes while the median delay for MECP2, SLC2A1, and other genes was ≥ 12 months. Conclusions: These data highlight the importance of comprehensive early testing in children with early-onset epilepsy.